Color converting method, density-gradient correction method and color printer using the same

Abstract

A method of color conversion includes preserving a 0% density for a particular color in the pre-conversion state to maintain a 0% density after conversion is provided via a translation table. Density gradation methods include a gradient value structure such that the highlight and shadow regions of the density are more finely represented in comparison to non-highlight and non-shadow regions. A further density correction method includes supplying an amount of energy to a non-image area when printing using a first color, wherein the amount of energy will not produce a dot in the non-image area upon application of a second color. A printer may employ one or more of the above methods in the form of a translation table or a density correction patch.

What is claimed is:  
     
       1. A color converting method comprising the step of: 
       performing three or more dimensional color conversion such that when at least one color of coloring materials has a halftone dot percentage of 0% in a state before the conversion, the at least one color keeps a halftone dot percentage of 0% after conversion,  
       wherein first X 1 , second X 2  and third X 3  coordinates correspond to axes of a Cartesian coordinate system, and wherein a fourth coordinate X 4  corresponds to a K value and wherein fifth X 5  and sixth X 6  coordinates correspond to reference axes lying in a plane of the Cartesian coordinate system, said conversion applied to at least three of said first through sixth coordinates.  
     
     
       2. The method of  claim 1 , wherein the conversion is applied to at least four of said first through sixth coordinates. 
     
     
       3. The method of  claim 1 , wherein the fourth and fifth coordinates correspond to respective planes where one of said first, second and third coordinates equals zero. 
     
     
       4. A color printer comprising: 
       a translation table with which color conversion is performed such that when at least one color of coloring materials has a halftone dot percentage of 0%, the energy for 0% gradient of the at least one color is fixed,  
       wherein first X 1 , second X 2  and third X 3  coordinates correspond to axes of a Cartesian coordinate system, and wherein a fourth coordinate X 4  corresponds to a K value and wherein fifth X 5  and sixth X 6  coordinates correspond to reference axes lying in a plane of the Cartesian coordinate system, said color conversion applied to at least three of said first through sixth coordinates.  
     
     
       5. The color printer according to  claim 4 , further comprising a thermal head for printing images based on energy levels supplied by said translation table. 
     
     
       6. The method of  claim 4 , wherein the conversion is applied to at least four of said first through sixth coordinates. 
     
     
       7. The method of  claim 4 , wherein the fourth and fifth coordinates correspond to respective planes where one of said first, second and third coordinates equals zero. 
     
     
       8. A printer comprising: 
       a halftone-dot area converting means for converting a first image information into a second image information having a set of halftone-dot areas which provide a gradation information of said first image information;  
       a gradation correction table for correcting said gradation information in which a difference in energy corresponding to a solid gradient of a shadow portion is larger than that corresponding to other gradients.  
     
     
       9. The printer according to  claim 8 , wherein said gradation correction table is defined in such a way that the difference in energy of a black color is larger than the differences of other colors. 
     
     
       10. A density gradient correction method comprising the step of: 
       performing density calibration by using a density calibration patch having a structure such that calibrations in a vicinity of a highlight portion and in a vicinity of a shadow portion are finely spaced in comparison with a non-highlight portion and a non-shadow portion.  
     
     
       11. A color printer comprising: 
       a density-calibration patch having a structure such that calibrations in a vicinity of a highlight portion and in a vicinity of a shadow portion are finely spaced in comparison with a non-highlight portion and a non-shadow portion.  
     
     
       12. A printer according to  claim 11 , further comprising: 
       a translation table with which color conversion is performed such that when at least one of color of coloring materials has a halftone dot percentage of 0%, the energy for a 0% gradient of the at least one color is fixed.  
     
     
       13. The color printer according to  claim 11 , further comprising a thermal head for printing images based on energy levels corresponding to density levels read from said density-calibration patch. 
     
     
       14. A density gradient correction method comprising the step of: 
       providing a margin width for a highlight portion and a margin width for a shadow portion, wherein the margin width for the highlight portion includes a first number of gradient values between a minimum gradient value and a gradient value corresponding to production of a 0% density, and wherein the margin width for the shadow portion includes a second number of gradient values between a maximum gradient value and a gradient value corresponding to production of a 100% density.  
     
     
       15. The density gradient correction method according to  claim 14 , wherein the margin width for the highlight portion is wider than that for the shadow portion. 
     
     
       16. A method according to any of claims  10  and  14 - 15  further comprising: 
       performing three or more dimension color conversion such that when at least one color of coloring materials has a halftone dot percentage of 0% in a state before the conversion, the at least one color keeps 0% after conversion.  
     
     
       17. A density gradient correction method comprising the step of: 
       supplying weak energy to a head corresponding to a non-image portion in a case of a primary color such that the intensity of a weak energy also does not cause a dot to be printed in the non-image portion in a case of a secondary or color.  
     
     
       18. A method according to any of claims  1 ,  10 ,  14 ,  15 , and  17 , further comprising forming an image using a thin-film thermal transfer method. 
     
     
       19. A method according to  claim 17  further comprising: 
       performing three or more dimensional color conversion such that when at least one color of coloring materials has a halftone dot percentage of 0% in a state before the conversion, the at least one color keeps a halftone dot percentage of 0% after conversion.  
     
     
       20. A color printer comprising: 
       a density gradient translation table for supplying weak energy to a head corresponding to a non-image portion in a case of a primary color such an intensity of the weak energy also does not cause a dot to be printed in the non-image portion in a case of a secondary color.  
     
     
       21. The printer according to any one of claims  4 ,  11  and  20  further including a thin-film thermal transfer imaging device. 
     
     
       22. A printer according to  claim 20  further comprising a translation table with which color conversion is performed such that when at least one color of coloring materials has a halftone dot percentage of 0%, the energy for a 0% gradient of the at least one color is fixed. 
     
     
       23. A color converting method comprising: 
       performing three or more dimensional color conversion such that when at least one color of coloring materials has a halftone dot percentage of 0% in a state before the conversion, the at least one color keeps a halftone dot percentage of 0% after conversion,  
       wherein a multidimensional coordinate correspond to X 1 , X 2 , . . ., and Xn axes of a Cartesian coordinate system, said n being an integer no less than three.  
     
     
       24. A color printer comprising: 
       a translation table with which multidimensional color conversion is performed such that when at least one color of coloring materials has a halftone dot percentage of 0%, the energy for 0% gradient of the at least one color is fixed,  
       wherein multidimensional coordinates correspond to X 1 , X 2 , . . ., and Xn axes of a Cartesian coordinate system, said n being an integer no less than three.